1. Field of the Invention
The present invention relates to a lithography apparatus and a pattern forming method using the same.
2. Description of the Related Art
A semiconductor technology remarkably developed for the recent ten years. The performance of the semiconductor has increased twice every eighteen month according to a so-called ‘Moore's law’ and what was like a dream yesterday has been realized today. A photolithography technology occupies a position at the backside of this rapid development. The photolithography is a crucial process technology in the semiconductor, for positioning a mask of a predetermined pattern on a wafer spread with a photo resist sensitive to light and illuminating light to form a mask shape. The photolithography is a crucial process occupying about 70% of the semiconductor realization process and remains one of the most important processes even in recent processes where a line width reduces.
The photolithography technology is applied as a technology for obtaining a predetermined pattern in the fields of a micro electronic, a micro electromechanical system (MEMS), and a biotechnology application.
The photolithography technology will be briefly described below. An energy-sensitive material called a resist is coated on a semiconductor wafer (e.g., a silicon wafer). A photo mask used in a semiconductor process has a mark carved in a film called a mask or a reticle, for position alignment of an image to be patterned with another image on another reticle. When light from a laser beam (generally, UV of a mercury arc lamp) light source passes through the patterned mask and is illuminated, an image of the mask pattern is created within the resist. After that, an exposed portion or a non-exposed portion of the resist is removed using a means such as a solution-based developer or a plasma etching, so that a patterned resist is created. Photolithography description is limited up to this point. After that, the developed pattern is used as a mask for etching in a subsequent process. The resist is removed afterwards. In the case of a plurality of devices, subsequent layers are formed and the process is repeated, so that upper patterns are formed within the devices. For manufacturing an integrated circuit (IC) device, the photolithography process is repeated using masks of 20 to 25 or more.
A problem the lithography technology faces during the device process is as follows. Since a high-speed operation and a low-power driving become possible as a line width is reduced, the semiconductor process is being oriented to the direction realizing a narrower line width. However, the most crucial problem in an exposure system that uses light as a list source is that diffraction of light gets serious as the line width gets narrow, which causes an error in the process and generates performance deterioration of the device.
The most fundamental method resolving this problem is to use a light source having a wavelength smaller than a pattern size. Alternatively, there is a projection lithography system that adopts a light source having a small wavelength and uses a reduction lens disposed between a mask and a substrate. It is possible to obtain a fine pattern and prevent diffraction of light from the light source even with the light source having a small wavelength using the reduction lens.
In the meantime, one of variables important as much as the light source in the lithography technology is a photo mask functioning as a film of a pattern, and an error with respect to a design measure should be minimized for accuracy of a result pattern. Therefore, an electron-beam (E-beam) lithography apparatus having no process error due to diffraction is used when the mask is manufactured. The process order is the same as the general lithography process order but a glass substrate or a quarz substrate having optical transmittance characteristics is used for the substrate and a polymethyl methacrylate (PMMA) (positive) for the E-beam is used for a photo sensitive agent. A surface where a PMMA pattern is carved is filled with Cr, and finally the photo sensitive agent is removed. The mask manufacture in this manner is called a hard mask. The hard mask is generally expensive and can be used in the exposure process more than two hundreds of times, and washing and inspection are required when repeatedly used. Besides, there are an emulsion mask or a film mask, which is cheap but has a disadvantage that it is difficult to use for a fine pattern.
Since such a photo mask requires a long time in manufacturing and has a fixed pattern shape, masks of different shapes are required for respective operations.
Accordingly, a manufacture cost of the mask increases. To overcome such a disadvantage, it should be possible to change the shape of the mask freely.
A liquid crystal (LC) panel is drawing attention as a candidate for a new mask meeting such a requirement. Since it is possible to freely change the image of the mask pattern using various image programs used in a computer and transmit the changed image to the LC panel in real-time, the LC panel has an advantage in viewpoint of cost and time in manufacturing the mask.
In the LC panel, a pixel is a basic unit and the LC contained in each of the pixel on/off-operates in response to an electric field to express a black and white. Electrode lines for applying an electric field are disposed in rows and columns of the pixel forming the LC panel. The portions of the electrode lines always remain transparent without an influence of the electric field. Therefore, one of the most crucial problems in using the LC panel for the mask is that a developed pattern is broken by pixel unit as is the shape of the portion of the electrode lines.
Accordingly, a variety of studies for overcoming the above problem are under progress.